1. Technical Field
The present invention relates to a power amplifier.
2. Description of the Related Art
In general, a power amplifier is a circuit which functions to amplify a low power signal, received from a transmitting part, to a high power signal at a preset center frequency f0 by using a nonlinear active element.
Since a power amplifier uses a nonlinear device, a signal is not output only at a preset frequency, but signals occur at the harmonic frequencies N×f0 of a preset frequency.
In this case, since harmonic frequencies affect the communication of other systems, the intensity of the harmonic frequencies is set for each of the systems.
Meanwhile, since a Complementary Metal-Oxide Semiconductor (CMOS) power amplifier generally uses a balance structure, it is implemented on an Integrated Passive Device (IPD) in the form of a transformer in order to reduce the loss of an output matching circuit.
A transformer used for the output matching of a power amplifier uses only a transformer and capacitors to transform output voltage.
Here, each of the capacitors is connected across both ends of each primary winding of the transformer and performs matching between input signals, and the secondary winding of the transformer is configured to sum power transmitted to the primary winding.
Since the conventional power amplifier configured as described above uses only a transformer and capacitors to transform output voltage, it can optimize output characteristics at a preset frequency, as shown in FIG. 1, but it cannot control output which is generated at harmonic frequencies by a nonlinear device, as shown in FIG. 2.